class Solution {
public:
    int search(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;

       while(left <= right)
        {
            int mid = left + (right - left) / 2;    // 防溢出
            if(nums[mid] < target)
                left = mid + 1;
            else if(nums[mid] > target)
                right = mid - 1;
            else
                return mid; // 找到了
        }
        return -1;  // 没有找到
    }
};